Self-cleaning oven

ABSTRACT

A conveyor oven having a first mode of operation and a second mode of operation is provided. The conveyor oven generally includes an oven chamber in which food is cooked, a conveyor moveable to convey the food through the oven chamber, a burner to generate heat for the oven chamber, the burner having a combustion airflow rate, at least one blower to circulate air within the oven chamber, and a controller. The blower operates at a first speed during the first mode of operation and at a second speed that is faster than the first speed during the second mode of operation. The controller is responsive to at least one of a burner output and an internal temperature of the oven chamber, and adjusts the combustion airflow rate based in part on at least one of the burner output and the internal temperature of the oven chamber.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/463,051, filed on May 8, 2009, which is a continuation of U.S. patentapplication Ser. No. 10/546,104, filed on Jul. 19, 2006, which is a U.S.National Phase Application of International Application No.PCT/US04/05153, filed Feb. 20, 2004, which claims priority of U.S.Provisional Patent Application No. 60/449,545, filed on Feb. 21, 2003.

U.S. patent application Ser. No. 12/463,051 published as U.S.Publication No. 2009/0223503 on Sep. 10, 2009; U.S. patent applicationSer. No. 10/546,104 published as U.S. Publication No. 2007/0006865 onJan. 11, 2007; and International Application No. PCT/US04/05153published as International Publication No. WO 2004/076928 on Sep. 10,2004. The entire contents of each of the foregoing applications andpublications are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a gas-fired tunnel oven, andparticularly a gas-fired conveyor oven.

BACKGROUND

Commercial, gas-fired tunnel ovens equipped with conveyors produce,among other things, pizzas, cookies, bread, cakes and donuts. Each ovenroutinely processes a large volume of food products and, as a result,becomes rather dirty. Bits of the food products themselves, burned foodproducts, and soot from the burners are typical sources of contaminationthat accumulate during use.

Gas-fired tunnel ovens traditionally have been cleaned manually withdetergent and acid solutions. The oven must be taken apart for cleaningby these methods. In addition to the oven walls, roof, and floor, theconveyor used with the tunnel oven must be cleaned, as well as anyjet-impingement convection fingers, convection blowers, and firedburners. Cleaning by the traditional methods is tedious and expensive.

SUMMARY

In theory, a gas-fired, commercially-sized tunnel oven might be cleanedby installing electrical heaters at critical points to raise theinternal temperature to a range that reduces virtually all contaminationto ash. In practice, cleaning a gas-fired tunnel oven by raising thetemperature with electrical heaters requires an estimated 50-100 amperesof electricity for each oven. Commercial bakers do not normally haveaccess to this much electrical current, and the cost of installing highcurrent electrical service is a significant financial barrier for mostbakers.

Accordingly, there is a need for a self-cleaning, gas-fired tunnel ovensuitable for use with a conveyor that can be cleaned without need ofdisassembly, manual cleaning, or detergents. Commercial bakers wouldwelcome a self-cleaning, gas-fired tunnel oven.

In some embodiments, a conveyor oven having a first mode of operationand a second mode of operation is provided. The conveyor oven generallyincludes an oven chamber in which food is cooked, a conveyor moveable toconvey the food through the oven chamber, a burner to generate heat forthe oven chamber, at least one blower to circulate air within the ovenchamber, and a controller. The burner has a combustion airflow rate. Theblower operates at a first speed during the first mode of operation andat a second speed that is faster than the first speed during the secondmode of operation. The controller is responsive to at least one of aburner output and an internal temperature of the oven chamber, andadjusts the combustion airflow rate based in part on at least one of theburner output and the internal temperature of the oven chamber.

Also, in some embodiments, a conveyor oven generally includes an ovenchamber in which food is cooked, a conveyor moveable to convey the foodthrough the oven chamber, a gas burner configured to generate heat forthe oven chamber, at least one blower to circulate air within the ovenchamber, and a controller. The gas burner has an adjustable combustionairflow rate and an adjustable gas flow rate. The controller isresponsive to at least one of a burner output and an internaltemperature of the oven chamber, adjusts the combustion airflow ratebased in part on at least one of the burner output and the internaltemperature of the oven chamber, and adjusts a speed of the blower basedin part on at least one of the burner output and the internaltemperature of the oven chamber.

Also, in some embodiments, a conveyor oven having a first mode ofoperation and a second mode of operation is provided, wherein theconveyor oven comprises an oven chamber in which food is cooked, aconveyor moveable to convey the food through the oven chamber, a gasburner configured to generate heat for the oven chamber, at least oneblower to circulate air within the oven, and a controller. The gasburner has a combustion airflow rate adjustable between the first andsecond modes of operation and a gas flow rate adjustable between thefirst and second modes of operation. The blower operates at a firstspeed during the first mode of operation and at a second speed differentfrom the first speed during the second mode of operation. The controlleris configured to adjust the combustion airflow rate and the gas flowrate to maintain a substantially constant ratio between the combustionairflow rate and the gas flow rate during both the first mode ofoperation and the second mode of operation.

Other aspects of the invention will become apparent by consideration ofthe detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a self-cleaning oven with both first andsecond conveyor extension sections extended, each of the conveyorsections being depicted without its mesh belt for clarity;

FIG. 2 is a partial perspective view of the oven of FIG. 1 showing adrive shaft, a main conveyor section and the first and second conveyorextension sections, each of the conveyor sections being depicted withoutits mesh belt for clarity;

FIG. 3 is a side view of the oven of FIG. 1 with one of the side wallsremoved, showing one of the blower and motor assemblies and twoair-impingement fingers;

FIG. 4 is a perspective view of the oven of FIG. 1 with the firstconveyor extension section extended and the second conveyor extensionsection retracted, the first conveyor extension section being shownwithout its mesh belt for clarity;

FIG. 5 is a view of the oven of FIG. 1 with the front access doorremoved, showing both conveyor extension sections in their retractedpositions;

FIG. 6 is a front elevation view of the oven of FIG. 1 with bothconveyor extension sections refracted;

FIG. 7 is an overhead perspective view of the oven of FIG. 1 with theceiling and overhead insulation removed, showing a roof-mounted burnerassembly, two blower and motor assemblies, and a vent arrangement;

FIG. 8 is a close-up perspective view of the burner assembly of FIG. 3showing a gas shut-off valve, a gas valve, an air valve, a valve linkthat coordinates the action of the gas valve with the action of the airvalve, and a burner;

FIG. 9 is a rear perspective view of the oven of FIG. 1 showing the twoblowers and the vent arrangement; and

FIG. 10 is a perspective view of walls and a tubular frame supportsurrounding a cooking chamber of the oven of FIG. 1.

FIG. 11 is a partial perspective view of the oven of FIG. 1 showing adrive shaft, the main conveyor section and the first conveyor extensionsection, each of the conveyors depicted without its mesh belt forclarity.

FIG. 12 is an overhead view of the oven of FIG. 1 with the ceiling andoverhead insulation removed, showing a roof-mounted flame tube assemblyand two blower and motor assemblies.

FIG. 13 is a view of the main conveyor section through an oven openingwith one of the conveyor extension sections removed.

FIG. 14 is a view of the main conveyor section and its connection to thefront wall of the oven depicted in FIG. 1.

FIG. 15 is a view of one of the conveyor extension sections separatedfrom the oven of FIG. 1.

FIG. 16 is a side view of the mesh belt of one of the conveyor extensionsections.

DETAILED DESCRIPTION

According to one embodiment, a pyrolytically self-cleaning, gas-fired,conveyor oven 10, as shown in FIG. 1, includes an oven housing 12supported on four legs 14. The oven housing 12 surrounds a cookingchamber 16 through which food products are passed on a conveyor assembly18. The oven 10 also includes a front access door 40 that can be openedusing a front access door handle 41.

As best seen in FIG. 2, the conveyor assembly 18 includes poweredrollers 20 that drive a wire mesh conveyor belt (not shown in theFigures) that conveys food through the cooking chamber 16. The poweredrollers 20 can be driven in either direction so that, as viewed in FIG.2, the conveyor belt can convey food through the cooking chamber 16 fromleft-to-right or right-to-left. Food products can be transported by theconveyor assembly 18 into a first oven opening 37 and out of a secondoven opening 38 or, alternatively, into the second oven opening 38 andout of the first oven opening 37. In either case, the motion of theconveyor drive motor (not shown) and, consequently, the motions of theconveyor assembly 18 are precisely and continuously controlled in orderto provide the optimum cooking time for the food products. The speed anddirection of the conveyor assembly 18 are input by an operator through acontrol station (not shown).

As the oven 10 is shown in FIGS. 1 and 2, it is configured for cookingfood products. That is, the conveyor assembly 18 extends out of thecooking chamber 16 at both ends. Food is placed on the conveyor assembly18 at either end of the oven 10 and is carried through the cookingchamber 16 to the other end of the oven 10. As best seen in FIG. 2, theconveyor assembly 18 includes a main conveyor section 30 and first andsecond conveyor extension sections 32, 34 extending out of the cookingchamber 16. Over time, as food products travel back and forth over theconveyor assembly 18, the various sections 30, 32, 34 of the conveyorassembly 18 clog with food debris and otherwise become dirty.Additionally, food particles that drop onto various surfaces andcomponents within the cooking chamber 16 become dirty. To clean the oven10, the first and second conveyor extension sections 32, 34 can bedisconnected from the main conveyor section 30 and inserted into thecooking chamber 16.

The main conveyor 30 is driven by a direct current electric motoroperating through a gear reducer. A pulse-controlled conveyor drivemotor (not shown) turns a drive shaft 86 which is rigidly attached to adrive gear 88, which are depicted in FIG. 11. The drive motor sendswell-defined pulses of electrical energy to move the drive shaft 86 ineither a clockwise or counterclockwise direction. Each electrical pulseof the motor moves the drive shaft 86 a reproducible increment. Forexample, a single pulse may be adjusted to advance the drive shaft 86 bya predetermined number of angular degrees. The frequency of electricalpules determines the speed of the drive shaft 86, and consequently thespeed of the conveyor assembly 18, in either direction. The drive gear88 turns the main conveyor section 30 and the first and second conveyorextension sections 32, 34 by means of follower gears 90, 92 (only one isshown for the first conveyor extension section 32). The follower gears90, 92 cause conveyor axles 110 to turn, which creates the conveyormotion. The speed of all the conveyor sections, and ultimately, thecooking time of food products traveling through the oven 10, isregulated by the drive motor. The drive motor for oven 10 is controlledby a digital control unit (not shown).

FIGS. 1 and 2 depict both the first conveyor extension section 32 andthe second conveyor extension section 34 in an extended and lockedposition, the conveyor extension sections 32, 34 being both collapsibleand extendable. The first conveyor extension section 32 is accompaniedby a first insulated door 35 and the second conveyor extension section34 is accompanied by a second insulated door 36. Both the first andsecond conveyor extension sections 32, 34 can be separated from the ovenhousing 12 and inserted into a first oven opening 37 and a second ovenopening 38, respectively. After the conveyor extension sections 32, 34have been inserted into the oven housing 12, the first insulated door 35can be shut to close the first oven opening 37 and the second insulateddoor 36 can be shut to close the second oven opening 38.

FIG. 11 is a partial perspective view of oven 10 in which only selectedcomponents are shown in order to better communicate the invention. FIG.11 shows the relationship of the main conveyor section 30 to the firstconveyor extension section 32 when the first conveyor extension section32 is in the extended position. The first and second conveyor extensionsections 32, 34 (only one is shown in FIG. 11) each include an uppernotch 78, sized and shaped to receive an upper peg 80, which is attachedto an inside wall of the oven (not shown in FIG. 11). The first andsecond conveyor extension sections 32, 34 also each include a lowernotch 82 for receiving a lower peg 84, which is also attached to theinside wall (not shown). Lifting the first and second conveyor extensionsections 32, 34 causes them to rotate about the upper pegs 80 until thelower pegs 84 disengage from the lower notches 82.

With the lower notches 82 disengaged, the first and second conveyorextension sections 32, 34 can be separated from oven 10 and insertedinto the first and second oven openings 37, 38 so that the first andsecond insulated doors 35, 36 close the first and second oven openings36, 38, as shown in FIG. 6.

In order to assemble the conveyor assembly 18 for baking, the firstconveyor section 32 is partially inserted into the first oven opening 37and locked in an extended position with respect to the main conveyorsection 30. The first conveyor section 32 is locked by inserting thepair of upper notches 78 formed by the sides of the first conveyorsection 32 under a pair of upper pegs 80 mounted in the oven 10. A pairof lower notches 82 also formed by the sides of the first conveyorextension 32 are then rotated onto a pair of lower pegs 84 mounted inthe oven 10. The second conveyor extension section 34 is similarlyinserted into the second oven opening 38 and locked in an extendedposition with respect to the main conveyor section 30.

The first conveyor extension section 32 is separated from the oven 10 inFIG. 13, providing a close-up view of the first oven opening 37 and themain conveyor section 30. The drive shaft 86 of the main conveyorsection 30 extends between two side plates 96, although only one of theside plates 96 is visible in FIG. 13. FIG. 13 also depicts five of thesix drive sprocket wheels 100 attached to the conveyor axle 110 of themain conveyor section 30. A mesh belt 102 is shown as an endless chainengaged with the drive sprocket wheels 100. One of the upper pegs 80 andone of the lower pegs 84, which cooperate for locking the first conveyorsection 32 (not shown in FIG. 13) in an extended position, are alsovisible in FIG. 13.

The sixth of the six drive sprocket wheels 100 of the main conveyorsection 30 is shown in FIG. 14 along with one of the two side plates 96.A bracket 106 extends from one of the side plates 96 and is fastened tothe front wall 66 for supporting the main conveyor section 30. The frontwall 66 also supports one of the upper pegs 80 and one of the lower pegs84.

A close-up, partial perspective view of the first conveyor extensionsection 32 is presented in FIG. 15. The mesh belt 102 of the firstconveyor extension section 32 tends to sag if not supported, asillustrated in FIG. 16. FIG. 15 depicts four guides 108, which areprovided to support the mesh belt 102. The guides 108 are in turnsupported by guide supports 98, which extend the width of the firstconveyor extension section 32. FIG. 15 also shows the conveyor axle 110and the six drive sprocket wheels 100 for the first conveyor section,which are used to facilitate the progress of the mesh belt 102.

FIG. 4 shows the second conveyor extension section 34 inserted into thecooking chamber 16 and a second insulated door 36 closed to seal off thesecond oven opening 38 through which the second conveyor extensionsection 34 previously extended.

FIG. 5 further illustrates that the main conveyor section 30 supportsthe first conveyor extension section 32 when the first conveyorextension section 32 is inserted into the first oven opening 37.Inserting the first conveyor extension section 32 into first ovenopening 37 allows the first insulated door 35 to close the first ovenopening 37. Similarly, the main conveyor section 30 supports the secondconveyor extension section 34, when the second conveyor extensionsection 34 is inserted into the second oven opening 38 so that thesecond insulated door 36 can close the second oven opening 38. With theinsulated doors 35, 36 closed, the cooking chamber 16 of the oven 10 iscompletely sealed, as shown in FIG. 6. The cooking chamber 16 can thenbe superheated to approximately 900°, turning all food debris in theoven 10 to ash. When the food debris has been burned and turned to ash,the front access door 40 can be opened using the front access doorhandle 41 and the ash can be cleaned from the oven 10.

As seen in FIGS. 13-16 each of conveyors includes endless stainlesssteel mesh belts 102 capable of traveling in either direction and atvariable speeds. Crumb trays (not shown) are removably installedunderneath the first and second conveyor extension sections 32, 34.

As food travels through the cooking chamber 16, it is cooked by theimpingement of hot air that is directed at the main conveyor section 30through nozzles 22 located on fingers 24. As shown in FIGS. 2 and 3, thedepicted conveyor oven 10 includes two fingers 24, a lower finger havingnozzles 22 directing air upward at the bottom of the conveyor assembly18 and an upper finger having nozzles 22 (not seen in FIG. 2) directingair downward at the top of the main conveyor section 30. The fingers 24contain an inner distributor plate (not shown) and a perforated outerplate containing the nozzles 22 that collimate the heated air and evenlydistribute the heated air across the main conveyor section 30 on whichthe food products ride. The oven 10 depicted in FIG. 3 includes twofingers 24 (one above the conveyor and one below), however, the oven 10can accommodate a number of bottom fingers 24 and top fingers 24. Anycombination or deletion of fingers may be employed.

The hot air directed through the fingers 24 is heated by a burnerassembly 42 (best seen in FIGS. 7 and 8) located under an instrumentpanel 39 (FIG. 1) on the front of the oven 10. The burner assembly 42creates the heat used by the oven 10 during both cooking (baking) andself-cleaning The burner assembly 42 heats the hot air that flowsthrough the fingers 24 to cook food products passing along the conveyorassembly 18. The burner assembly 42 burns a gas and air mixture at aburner 44, which shoots a flame down a flame tube 46. The flame heatsthe air contained in the flame tube 46, and the heated air exits theflame tube through an outlet 47 and into a plenum 94, as seen in FIG.12. The open space of the plenum 94, located in front of the back wall70 of the oven 10, provides the hot air with a directed passagewaytoward a blower housing 74 where it will be circulated throughout thecooking chamber 16.

Because the burner 44 is called upon to satisfy a wide range of heatoutput requirements, it is necessary to control the flow of gas and airsupplied to the burner 44. While the burner 44 is operating, the flow ofboth air and heating gas to the burner 44 is modulated by a combinedcontrol system. With this combined modulating control system forcombustion air and heating gas, optimum combustion conditions within theburner 44 can be maintained approximately constant over a range of heatoutputs. With this combined modulating control system, the ratio ofcombustion air flow to heating gas flow can be optimized and maintainedso that combustion is thermally efficient and environmentally sound,producing a minimum of objectionable byproducts.

The ratio of combustion air to heating gas can be optimized to produce,for example, environmentally clean burning and the ratio will remainclose to the optimum value whether the programmable controller (notshown) calls for high heat or low heat. Alternatively, the ratio may beoptimized for optimal fuel consumption, optimal heat-up time or anyother results that the operator desires and the ratio will not varysubstantially with heat output. This modulating control system forcombustion air and heating gas over a range of heat output is especiallyadvantageous for a self-cleaning oven, such as the oven 10, where arange of heat outputs is required.

The burner assembly 42 includes an actuator 48 that operates an airvalve 50 that regulates the amount of air entering the burner 44 from acombustion air blower 52. The actuator 48 controls the position of theair valve 50 based on signals received from other control instrumentsand sensors (not shown) included in oven 10. A valve link 54 coordinatesthe movement of the gas valve 56 with that of the air valve 50. The gasvalve 56 receives gas from an automatic gas shut-off valve 57 andmodulates the flow of this gas so that the ratio of heating gas tocombustion air is relatively constant for a wide range of heating loads.The valve link 54 connects the air valve 50 to the gas valve 56 so thatas the actuator 48 opens and closes the air valve 50, the gas valve 56is correspondingly opened and closed, proportionally mixing the air andgas as they enter the burner 44. The air and gas mixture is then ignitedinside the burner 44 and a flame shoots down the flame tube 46.

One of the advantages of modulating air and gas control, as provided bythe valve link 54, is that the amount of excess air in the flame tube 46remains substantially the same during high and low heating load periods.This advantage is particularly important in a self-cleaning, pyroliticoven, which exhibits a significantly higher heating load duringself-cleaning than conventional cooking heating loads. Although thevalve link 54 depicted in FIGS. 6, 7 and 8 is mechanical, it is alsocontemplated that the positions of an air valve and a gas valve inmodulating air and gas control systems may alternatively be coordinatedby, for example, utilizing electronically-controlled actuators for eachof the valves and coordinating their positions by means of one or moreelectronic controllers.

The burner 44 may be mounted anywhere in the oven. Preferably, theburner 44 is roof-mounted as shown and sends its flame along the insideof the flame tube 46 mounted adjacent the ceiling of the oven 10. Duringoperation of the oven 10, contaminants tend to accumulate most heavilyon and near the oven floors. Thus, the roof-mounted burner system ismore likely to progressively incinerate—and less likely to ignite—thefloor accumulation as compared to conventional floor-mounted andwall-mounted burner configurations.

During baking and self-cleaning operations, the flame tube 46 becomesvery hot and radiates heat energy throughout the inventive oven 10. Itis contemplated that a diffusing tube (not shown) may be employed aroundthe burner for processing food products that tend to discolor orotherwise deteriorate when subjected to intense radiant heat.

The oven 10 has two relatively large blowers 26, 27 (see FIG. 7) to movethe heated air created by the burner 44 through the fingers 24 and ontothe product so that the most efficient bake is achieved for each foodproduct processed in the oven 10. More specifically, the oven 10 employscollimated, vertical air streams to give uniform and intensive heating.The collimated, vertical streams of air that emerge from the fingers 24provide an exceptional heat transfer rate and generally bake foodsfaster and at lower temperatures than in conventional convection hot airor infrared heating ovens.

The hot air is circulated through the oven 10 by the two blowers 26, 27located at the back of the oven 10 (see FIG. 9). The two convectionblowers 26, 27 are located in the blower housing 74 (see FIG. 10). Theblowers 26, 27 are each powered by a blower motor 75 (only one is shownin FIG. 9), which is mounted on the back wall 70, and connected to theblowers 26, 27 by a shaft (not shown). In order to protect the shaftsfrom the pyrolitic temperature of the self-cleaning operation, theshafts may be fitted with heat-slingers (not shown) or other coolingapparatuses. A heat slinger is a type of fan arrangement mounted on theshaft. Each blower motor 75 may be equipped with a dedicated speedcontroller (not shown), preferably including an electrical powerinverter. With the benefit of individual speed control, the blowers 26,27 can be individually accelerated and decelerated to optimizeelectrical current inrush, the burner 44 firing or convective heat loss.The speed of the blowers 26, 27 may also be individually controlled inorder to create distinguishable heating zones within the oven 10 tooptimize the baking of particular food products.

In another embodiment, the blowers 26, 27 may be variable speed blowersthat are controlled together so that their speeds, while variable, arealways the same as each other.

There are also two cooling fans 13, 15 located on the front of oven 10as depicted in FIGS. 1, 4, 6, and 7. These fans blow cool air in throughthe machinery compartment and out the side walls. The cooling fans 13,15 draw air from the surroundings through the instrument panel 39 forcooling the instruments located behind the instrument panel 39. Aportion of the discharge air from the cooling fans 13, 15 may enter thecombustion air blower 52 and be delivered to the burner 44 as combustionair. The remainder of the discharge air from cooling fans 13, 15 enterspassages that extend between the external sheeting of the oven 10 and aninside wall, which supports insulation. The flow of air in thesepassages serves to cool the external sheeting of the oven 10 belowpreferably about 125 degrees F.

Referring to FIG. 9, a vent arrangement 58 is located at the back of theoven 10. The vent arrangement 58 includes a vent valve 60 that ispositioned between a vent tube 62 and a T-shaped tube 64 thatcommunicates with the high-pressure sides of the blowers 26. During anormal cooking cycle, the vent valve 60 is closed so that no air passesthrough the vent valve 60 into the vent tube 62. In this way, duringcooking, air that is heated is directed solely into the cooking chamber16 for efficient cooking of food in the cooking chamber 16. However,when it is desired to clean the oven 10, the vent valve 60 is opened andthe oven openings 37, 38 are closed, as discussed above. By opening thevent valve 60, enough heated air is exhausted through the vent tube 62to maintain a slight negative pressure within the cooking chamber 16. Inthis way, the smoke and soot that develops during a self-cleaning cycleis exhausted through the vent tube 62 and the passage of smoke and sootthrough small openings and cracks in the oven housing 12 is prevented.

As shown in FIG. 10, the cooking chamber 16 is bounded by a front wall66 and two side walls 68 that are connected to a back wall 70. The frontwall 66, two side walls 68, and back wall 70 are all screwed together toform a box surrounding the cooking chamber 16. The back wall 70 of thisbox is fixed to a tubular frame 71, which is connected to a platform 72.However, while the back wall 70 of the box is fixed to the tubular frame71, the front wall 66, and two side walls 68 are free-floating. That is,the front wall 66 and two side walls 68 are connected to the back wall70, but are not connected to the tubular frame 71. The perimeters of thefront wall 66 and the two side walls 68 include lips 73 that sit on thevarious members that make up the tubular frame 71, but are not fixedlyconnected to those members. In this way, the front wall 66 and two sidewalls 68 are free to move relative to the tubular frame 71 so thatduring cooking, and particularly during self-cleaning when thetemperatures in the cooking chamber 16 are relatively high, the frontwall 66 and side walls 68 of the cooking chamber 16 are free to expandand slide on the members of the tubular frame 71, thereby preventingbuckling and warping of the walls of the cooking chamber 16.

A unified display control station (not shown) for the oven 10 caninclude a blower selector, a heat selector, a conveyor selector, two ormore conveyor speed controllers and a digital temperature controller.Additionally, a machinery compartment access panel safety switchdisconnects electrical power to the controls and the blowers when themachinery compartment access panel is opened.

In order to start up the oven 10, an operator confirms that the frontaccess door 40 is closed. The operator then turns the blower andconveyor selectors to the “on” position. If necessary, the operatoradjusts the conveyor speed setting by pushing appropriate selectors onthe conveyor speed controller. The operator adjusts the temperaturecontroller to a desired temperature and selects normal operation. A heatswitch on a control station (not shown) of the oven 10 activates thecombustion air blower 52. The burner 44 is a direct ignition burner. Themain gas valve 57 is opened while starting a spark in the burner 44. Asensor then monitors whether a flame is present within the burner 44. Ifa flame is not detected within 6 seconds, the main gas valve 57 is shutdown, the burner 44 is purged, and the ignition cycle is repeated.Referring to FIGS. 7 and 8, a gas bypass tube 76 provides enough gas tothe burner 44 to maintain a minimum flame even when the gas modulationvalve 56 is closed.

The oven 10 will typically heat to a desired heating set-pointtemperature within a matter of minutes. While the oven 10 is heating,the control station (not shown) displays the actual temperature. One ormore thermocouples (not shown) in the interior of the oven 10 sendsignals to a programmable controller (not shown) that controls theactuator 48. If the programmable controller (not shown) calls for moreheat, the actuator 48 rotates to open the air valve 50 and morecombustion air is permitted to pass from the combustion air blower 52 tothe burner 44. Simultaneously, the valve link 54 moves under theinfluence of the actuator 48 to further open the gas valve 56,permitting more heating gas to pass from gas line 55 to the burner 44.If the programmable controller (not shown) calls for less heat, thevalve link 54 causes the air valve 50 and the gas valve 56 to closesimultaneously and proportionally. Consequently, the ratio of combustionair flow to heating gas flow entering the burner 44 remainsapproximately constant over a range of heat output.

As mentioned, the speed of the blowers 26, 27 can be varied. Forexample, the speed of the blowers may be two-thirds full speed duringstart-up and self-cleaning cycles and full speed during a cooking cycleto promote heating efficiency during each of the cycles. For heating theoven 10 to baking or self-cleaning temperatures, one or both of theblower motors 75 (only one is shown in FIG. 9) start and routinely rampup to a desired operating speed in a programmable period of time.Programming the start-up time of convection blower motors 75 makesfiring of the burner 44 more reliable and promotes better combustion,among other things. When the blowers 26, 27 are turning, the burner 44is initially fired with a minimum heat output and ramped up to thebaking or self-cleaning heat output over a period of time by, forexample, a programmable controller (not shown). When the desired heatoutput has been achieved, the blower motors 75 are accelerated tooperating speed in a programmable period of time.

The start-up procedure (i.e., ramping up the speed of one or both of theblowers 26, 27) prevents an objectionable current inrush situation thatis observed in conventional ovens, which commonly start two or moreblower motors at full speed simultaneously. This startup procedure isalso quieter, and requires less electricity and heating gas, than thestartup of conventional ovens. Because the blowers 26, 27 draw moreelectrical current when the oven is cold and the air in the oven isrelatively dense, operating both blowers at low speed during heat-up(start-up) saves electricity. Also, because increased convection on theinside surfaces of the oven walls promotes heat loss to the kitchen,operating only one of the convection blowers during heat-up savesheating gas.

Preferably, each of the blowers 26, 27 is equipped with an electricalpower inverter (not shown), which alters the frequency and/or voltage ofthe electrical current to control the speed of the blower 26 or 27. Inthat case, the blower motor 75 can be either ramped up to operatingspeed over a programmable period such as, for example, about thirtyminutes, or held at an optimal intermediate speed until the oven 10reaches baking or cleaning temperature and then accelerated. Thesevariations conserve still more energy by providing appropriateprogrammable blower speeds depending on the current operation of theoven 10. When the oven 10 is, for example, baking (cooking),self-cleaning, warming up, or cooling down, the blowers 26, 27 canoperate at specific speeds best suited for each individual activity.

Furthermore, for baking, the speed of the blower motors 75 (only one isshown in FIG. 9) may be separately adjusted to create two or moredifferent heating zones (not shown) within the oven 10. These heatingzones (not shown) can be created at will and utilized to optimize thebaking process and, consequently, the finished quality of a particularfood product. The oven 10 may be equipped with two or more thermocouples(not shown) or other temperature sensors to individually monitor andadjust these heating zones (not shown). The manner in which the signalsfrom these thermocouples (not shown) are averaged or otherwiseinterpreted by the programmable controller can be varied to suit thefood product.

In order to shut down the blowers 26, 27, the operator selects standbyon the control station. The blowers 26, 27 will remain in operationuntil the oven 10 has cooled to below 200 degrees F. and then ceaseturning.

When it is determined that the oven 10 should be cleaned, it is cooledto a temperature below about 140 degrees F. The operator then disengagesthe first conveyor extension section 32 and withdraws the first conveyorextension section 32 from the first oven opening 37. The first conveyorextension section 32 is then inserted into the first oven opening 37 sothat the first conveyor extension section 32 is supported by the mainconveyor section 30 and the first insulated door 35 closes the firstoven opening 37. The second conveyor extension section 34 is similarlyseparated from the oven 10 and inserted into the second oven opening 38and the second insulated door 36 is closed. Because the first and secondconveyor extension sections 32, 34 are inserted into the interior of theoven 10, they are cleaned by pyrolitic heat during the self-cleaningcycle. The vent valve 60 (best seen in FIG. 9) is opened and the blowers26, 27 are then brought up to operating speed and the burner 44 is firedto raise the oven 10 to self-cleaning temperature. During theself-cleaning cycle, oven 10 operates under the control of temperaturesensors and controllers (not shown) that are specifically designed tooperate in the range of about 650-1000 degrees F. These may be the samesensors and controllers used for baking (not shown) or a separate set.

In either case, the programmable control system actuates a set of safetyinterlocks adapted for cleaning temperature operation. For example, theoven overrides the baking cycle high temperature shutdown limits, whichare typically set at values less than 600 degrees F. As another example,the programmable control system actuates door locks that deter peoplefrom opening the oven doors during the pyrolitic self-cleaning cycle.

The programmable controller also initiates corrective action if unsafeor undesirable conditions are detected. For example, upon detectingexcessively high temperatures, high smoke levels or low oxygen levelswithin the oven, the programmable controller shuts down the burner 44and the blowers 26, 27.

As mentioned, during cleaning, the interior of the oven 10 is kept undera negative pressure compared to the surrounding atmospheric pressure. Inthe illustrated embodiment the opening of the vent valve 60 and theoperation of the blowers 26, 27 create the negative pressure in theinterior of the oven 10. As mentioned earlier, when the vent valve 60 isopened and the blowers 26, 27 are operating, enough circulating hot airescapes through the vent valve 60 to create the negative pressure insidethe cooking chamber 16 necessary to force the smoke and soot createdduring the cleaning cycle through the vent tube 62. In anotherembodiment, an inducer blower (not shown) maintains the interior of theoven 10 under a negative pressure during cleaning as compared to thesurrounding atmospheric pressure. The inducer blower creates thisnegative pressure by drawing air from the blower housing 74. The blowers26, 27 actually assist the inducer blower in creating this negativepressure because the discharge flow from the blowers 26, 27 is impelleddirectly into the inducer blower. The combined effect is similar to thatof a two-stage blower. The discharge flow from the inducer blower issent to the vent arrangement 58.

The inducer blower could also take suction from the interior of the oven10 during normal baking The entry of the inducer blower opens directlyinto the blower housing 74. The inducer blower may be positioneddirectly in the path of the discharge air flow from each of the blowers26, 27 so that the two sets of blowers work in tandem to reduce thepressure in the interior of the oven 10. Alternatively, the inducerblower may be mounted anywhere in the interior of the oven 10. Thedischarge flow of air from the inducer blower is sent to the ventarrangement 58 for disposal.

Maintaining negative pressure in the interior of the oven 10 during bothcooking and self-cleaning enhances energy efficiency and safety.Maintaining negative pressure in the interior of the oven 10 during thecooking and self-cleaning operations insures that little or no heatedair escapes to the kitchen. Minimizing heated air loss makes the oven 10more energy efficient. Any loss or discharge of heated air from theinterior of the oven 10 necessitates the combustion of additionalheating gas. By directing all exhaust flows from the oven 10 to the ventarrangement 58 and ultimately the vent tube 62, the loss or discharge ofheated air can be better controlled and minimized. Also, the negativepressure system promotes safety because negative pressure retainsburning gases in the interior of the oven 10 rather than permitting themto escape into the kitchen. Additionally, maintaining negative pressurein the oven 10 tends to prevent any smoky residue from building up onthe exterior of the oven 10 during normal cooking and self-cleaningoperations. The exterior surfaces of the oven 10 remain clean longerbecause they are not subjected to smoke, which commonly escapes from theatmospheric cooking chambers of conventional ovens.

The blowers 26, 27 turn at a relatively low speed during a firstincineration period of the cleaning cycle. This low speed uniformlydistributes heat throughout the interior of the oven 10 while minimizingconvective heat loss through the walls of the oven 10. The firstincineration period generally continues for about one hour, although itmay be longer or shorter based on factors such as the cleaningtemperature and the amount and type of contamination in the oven 10.

During a second incineration period, which is generally about one tothree hours in duration, the blowers 26, 27 operate at a relativelyhigher speed to promote complete incineration of the contamination ordebris accumulation. The temperature of the oven 10 is increased to apeak temperature at least once during the second incineration period.

After the incineration periods, the programmable controller cools theoven, disengages the safety interlocks and arranges the control systemfor cooking operation. Due to the combination of high temperature andconvective air flow in the inventive oven during the self-cleaningcycle, any contamination accumulation that is in the oven is reduced toharmless and sterile ash. This ash may be collected on drip pansprovided for that purpose, which can be accessed through the frontaccess door 40 and carried away to disposal. Alternatively, the ash maybe collected in a vacuum cleaner system that is built into orindependent of the inventive oven.

It is contemplated that collection of the ash from the lower fingers maybe facilitated by constructing the mesh belt 102 of the main conveyorsection 30 so that it is close to or touching the perforated plates ofthe lower fingers 24. The mesh belt 102 thus pushes or scrapes the ashfrom the lower fingers 24 for collection by a drip pan or vacuum system.Preferably, the perforations are formed so that the lower fingers 24present a nonabrasive surface to the mesh belt 102.

Although the invention has been described in detail with reference tocertain preferred embodiments, variations and modifications exist withinthe scope and spirit of the invention as described and defined in thefollowing claims.

1. A conveyor oven having a first mode of operation and second mode ofoperation, the conveyor oven comprising: an oven chamber in which foodis cooked; a conveyor moveable to convey the food through the ovenchamber; a burner to generate heat for the oven chamber, the burnerhaving a combustion airflow rate; at least one blower to circulate airwithin the oven chamber, wherein the blower operates at a first speedduring the first mode of operation and at a second speed that is fasterthan the first speed during the second mode of operation; and acontroller that is responsive to at least one of a burner output and aninternal temperature of the oven chamber, and adjusts the combustionairflow rate based in part on at least one of the burner output and theinternal temperature of the oven chamber.
 2. The conveyor oven of claim1, further comprising a valve for adjusting the combustion airflow rate.3. The conveyor oven of claim 1, wherein the speed of the blower isbased at least in part on the internal temperature of the oven chamber.4. The conveyor oven of claim 1, wherein the speed of the blower isbased at least in part on the burner output.
 5. The conveyor oven ofclaim 1, wherein the burner output is greater in the second mode ofoperation than in the first mode of operation.
 6. The conveyor oven ofclaim 1, wherein the second mode of operation is a cooking mode.
 7. Theconveyor oven of claim 1, wherein the blower speed is adjusted betweenthe first mode of operation and the second mode of operation when adesired heat output of the burner has been achieved.
 8. The conveyoroven of claim 1, wherein the burner has a gas flow rate that is adjustedbased in part on at least one of the burner output and the internaltemperature of the oven chamber.
 9. The conveyor oven of claim 8,wherein the controller adjusts the combustion airflow rate and theburner gas flow rate to maintain a substantially constant ratio betweenthe combustion airflow rate and the gas flow rate during both the firstmode of operation and the second mode of operation.
 10. The conveyoroven of claim 1 further comprising two burners, wherein the two burnersare separately adjustable to create two different heating zones in theoven chamber.
 11. A conveyor oven comprising: an oven chamber in whichfood is cooked; a conveyor moveable to convey the food through the ovenchamber; a gas burner configured to generate heat for the oven chamber,the gas burner having an adjustable combustion airflow rate and anadjustable gas flow rate; at least one blower to circulate air withinthe oven chamber; and a controller that is responsive to at least one ofa burner output and an internal temperature of the oven chamber, adjuststhe combustion airflow rate based in part on at least one of the burneroutput and the internal temperature of the oven chamber, and adjusts aspeed of the blower based in part on at least one of the burner outputand the internal temperature of the oven chamber.
 12. The conveyor ovenof claim 11, wherein the controller adjusts the gas flow rate based atleast in part on one of the burner output and the internal temperatureof the oven chamber.
 13. The conveyor oven of claim 11, wherein thecontroller adjusts the combustion airflow rate and the gas flow rate tomaintain a substantially constant ratio between the combustion airflowrate and the gas flow rate.
 14. The conveyor oven of claim 11, furthercomprising a valve configured to adjust the burner airflow rate.
 15. Aconveyor oven having a first mode of operation and a second mode ofoperation, the conveyor oven comprising: an oven chamber in which foodis cooked; a conveyor moveable to convey the food through the ovenchamber; a gas burner configured to generate heat for the oven chamber,the gas burner having a combustion airflow rate adjustable between thefirst and second modes of operation and a gas flow rate adjustablebetween the first and second modes of operation; at least one blower tocirculate air within the oven, wherein the blower operates at a firstspeed during the first mode of operation and at a second speed differentfrom the first speed during the second mode of operation; and acontroller configured to adjust the combustion airflow rate and the gasflow rate to maintain a substantially constant ratio between thecombustion airflow rate and the gas flow rate during both the first modeof operation and the second mode of operation.
 16. The conveyor oven ofclaim 15, wherein the combustion airflow rate and the gas flow rate areincreased in the second mode of operation from the first mode ofoperation.
 17. The conveyor oven of claim 15, wherein the bloweroperates at a higher speed in the second mode of operation than in thefirst mode of operation.
 18. The conveyor oven of claim 15, furthercomprising a valve configured to adjust the combustion airflow rate. 19.The conveyor oven of claim 15, wherein one of the first mode ofoperation and the second mode of operation is a cooking mode.
 20. Theconveyor oven of claim 15, wherein the second mode of operation is acooking mode.